The invention relates to a cutting tool for the machining of wood or a wood-based material, in particular a wood composite material, or a plastic, and also to a method for the manufacture of a cutting tool in accordance with the pre-characterising part of the independent claim in the respective category.
The manufacture of efficient tools and components is mostly realised by a coating of their surfaces. An important class of such coated substrates are tools, among others in particular chip forming cutting tools, and above all cutting tools in the field of the machining of wood or the machining of plastics. In this connection rotating cutting tools or rotary cutting tools for the machining of wood or wood-based composite material or of plastics are of particular interest, since these often rotate at very high rotary speeds in the operating state and for this reason are exposed to very high mechanical and thermal stresses, in particular in the region of the cutting edges. Typical substrate materials of tools which are coated, are among other things tool steels and hard metals, but also all other possible substrate materials.
Since the use of wood and plastics as materials has increased more and more in recent years and wood, or wood-based materials and plastics are becoming more and more attractive in the market place, the demand for tools for the reliable machining of the materials wood and plastic has risen correspondingly. In this connection, within the scope of this invention, plastics are to be understood to be all usual plastics, known to the person averagely skilled in the art, such as plastic, synthetic composite materials, elastomers, rubber, in particular hard rubber combination materials made of wood and plastics etc.
This applies to a special degree, but not only, to the lamination industry where for example materials with a relatively small diameter and short length are laminated in order to manufacture larger planks or boards or for the further processing of certain materials of larger diameter. Due to ever growing demands on quality, however also for reasons of reliability and economy in the use of the corresponding tools, there is an increasing demand for tools of which the highly loaded cutting edges are appropriately refined on the surfaces which come into direct contact with the material to be processed, wood or plastic.
Such tools are dovetail cutters for example, a tool which is used in the manufacture of laminate boards to produce a dovetail-like joint which, it goes without saying, has to be incorporated into every board as identically as possible, which makes the highest demands on the precision of the tool.
Comparable demands are made on saws provided with tips for example, with which solid blocks, beams or boards have to be sawed for example, however also drills, milling cutters, shape cutters and numerous other tools for plastic and wood machining are further prominent examples.
The service life of the tool also naturally plays an important role, i.e. the time which a tool such as this can be used, until either a cutting edge of the tool has to be reground for example or the cutting edge or the tool as a whole has to be exchanged for a not used tool.
The thickness of the saw blades for example should also be kept to the minimum, so that, on the one hand, as little plastic or wood in the form of sawdust as possible is consumed during sawing and, on the other hand, a high precision is achievable in the machining, e.g in order to produce ever smaller structures. In this connection a situation has to be prevented at the same time in which the tool enters instable operating conditions due to lack of thickness, so that for example in the case of a sawing tool a predetermined machining path can no longer be adhered to, or the tool breaks or cracks due to high stresses.
A further important point relates to the appearance and workmanship of the surface of such cutting tools. It is known that when machining plastics, wood or wood-based materials, deposits of plastic particles, resin-containing or resin-like deposits, or deposits which contain rubber, adhesives, rubber solutions, preservatives of all kinds or other organic or inorganic components of the plastic or wood material or wood composite material to be machined can occur on the surfaces of the cutting tools. If, for example, a plastic or a wood material or a wood composite material is cut, the aforementioned components of the material, which are scattered during cutting, can deposit on the cutting tool. In particular in the region of the cutting edge, the deposited components can solidify and increasingly further deposit. This phenomenon is called the deposition of “gum” in technical terminology, with “gum” not only meaning rubber-like deposits but all deposits which have already been named in part in the above by way of example, which can occur in the machining of plastics and wood materials with cutting tools.
As a rule these deposits of gum are independent of the sharpness of the blade and occur even when the blade is still new and unused. In this connection the deposits are not only present in a deposited and accumulated state, but also in a densely solidified state, which presumably develops by hardening due to polymerisation processes or other, also thermally caused processes of certain components of the plastic or of the wood material. In this connection the deposits are often so tenacious that they can hardly be removed using mechanical or other means, so that the cutting tool becomes unusable due to the deposits and has to be exchanged, although the cutting edge per se is still sufficiently sharp.
In certain cases it is possible in this connection to detach the deposits by means of different solvents, which is naturally time-consuming and correspondingly expensive.
This and further problems, for example in relation to a too great roughness of the surface which, on the one hand, further favours the deposits and, on the other hand, leads to an undesired high friction during the cutting process between the cutting tool and a material which is to be machined, have been known for a long time and have already been discussed in part for the case of wood composite materials in DE 694 25 277 T3 for example, the content of which is hereby incorporated into the present application in its entirety.
With relation to the surface appearance and workmanship of the cutting tools, DE 694 25 277 T3 proposes providing an outermost surface of the flank of a side cutting edge with a coating, which is formed from chromium or a chromium compound with a nitride, a carbide, a carbon nitride or a carbo-nitride.
This means that the authors of DE 694 25 277 T3 propose the application of a pure chromium coating as the outermost coating on a cutting edge of a cutting tool either by means of hard chroming, or depositing CrN, or a compound containing chromium and carbon or a compound containing chromium, carbon and nitrogen, by means of a physical vapour deposition method (PVD) wherein, in relation to chromium compounds, only the characteristics of the surfaces were actually discussed, which either comprise pure chromium or CrN.
These layers discussed in DE 694 25 277 may possibly offer a certain improvement relative to the rest of the prior art. However in practice three decisive disadvantages have emerged.
First of all these layers can not prevent the deposition of the gum defined more closely above to an adequate extent in all cases. A second fundamental disadvantage is that the methods for the generation of the surfaces on the tools proposed in DE 694 25 277 T3 are partly problematic from the point of view of the environment. Thus hard chroming is, as is known, an electrochemical process with questionable effects on the working environment and correspondingly problematic waste products. Thirdly, these tools are only suitable for the machining of wood-based products and not suitable for the machining of plastics.
Furthermore, some completely different methods such as hard chroming and PVD, have to be combined for the generation of the combination layers described in DE 694 25 277 T3, which makes the coating methods time-consuming and expensive.